(1) Field of the Invention
The present invention relates to an apparatus for controllably sucking intake air into each cylinder of an internal combustion engine and a method for controlling intake air quantity of the internal combustion engine with improved responsive characteristic.
(2) Description of the Background Art
Recently, a generally called traction control system (TCS) has been put into practice which is provided with an auxiliary throttle valve installed within a throttle chamber of an intake air passage of a vehicular engine in series with a first throttle valve (installed within the throttle chamber) associated with an accelerator pedal, the auxiliary throttle valve being driven by means of an electric motor which pivots the auxiliary throttle valve in response to a control signal.
The traction control system further includes a first sensor for detecting a rotational speed of each driven tire wheel of the vehicle, a second sensor for detecting a rotational speed of each non-driven (steered) tire wheel, and calculation means for calculating a difference between both rotational speeds of the driven and non-driven wheels to monitor a slip condition. Then, the traction control system controls an opening angle of the auxiliary throttle valve toward a closed position when the slip condition appears so that the engine output is reduced, and an excessive intake air quantity caused by the instantaneous opening angle of the first throttle valve is throttled by means of the auxiliary throttle valve.
Such a traction control system as described above is exemplified by U.S. Pat. Nos. 4,850,659, 4,811,808, 4,765,430, and 4,969,102.
In order to cope with a recent trend of requiring a low fuel consumption rate for the vehicular engine, a control system having an increased Exhaust Gas Recirculation rate (EGR) and/or an air/fuel mixture ratio which is controlled to become leaner, has been proposed.
However, if the controls for increasing the EGR rate and/or making the air/fuel mixture ratio leaner are executed, a surge, i.e., a low frequency vibration of a vehicle body in the forward and rearward directions during a cruise run or during a vehicle acceleration/deceleration due to an unsmooth operation of the vehicular engine, can occur easily.
If the surge were absorbed and eliminated by the opening angle control of the auxiliary throttle valve in the traction control system described above, the surge could be avoided and, on the other hand, a low fuel consumption rate could be achieved through the leaner air/fuel mixture ratio.
However, such a traction control as described above has an adverse effect on the engine output characteristic. That is to say, even if the surge, having a frequency range from 1 Hz to 10 Hz which is transmitted to an occupant of the vehicle, is absorbed through the opening angle control of the auxiliary throttle valve, the responsive characteristic of the engine output to the controlled opening angle of the auxiliary throttle valve is poor due to an inherent presence of a collector (intake manifold which is chamber) capacity in an intake manifold provided at a downstream portion of the auxiliary throttle valve. Therefore, the surge cannot sufficiently be absorbed in the above-described traction control system.
In addition, in an engine output control using the traction control system such that the engine output is reduced when the slip condition occurs, the traction on the wheels of the vehicle cannot speedily recover due to the presence of a response delay to the controlled opening angle of the auxiliary throttle valve in the engine output. The response delay being caused by the presence of the collector capacity described above.
Although the auxiliary throttle valve can be used to control the engine output, irrespective of the opening angle of the first throttle valve controlled in association with the accelerator pedal operation, such that the engine output is once reduced during a gear shift (for example, gear range up-shift from a third gear range to a fourth gear range) of a gear range of a vehicular power transmission associated with the engine in order to reduce or relieve a shock occurred during the gear shift operation, the responsive characteristic of the engine output to the controlled opening angle control of the auxiliary throttle valve is poor. It is desirable and necessary to improve such a poor responsive characteristic if such an engine output control system is put into practice.
Furthermore, in a case where an opening angle of an idling speed control valve, intervened in a bypass passage bypassing the first and auxiliary throttle valves, is controlled so that an engine idling revolutional speed is matched with a target idling revolutional speed in a feedback control mode, the intake air supplied via the bypass passage is once filled in the intake manifold collector portion and, then, sucked into the engine.
Therefore, a response delay also occurs during idling speed control through the idling speed control valve in the same way as the response delay in the engine output control through the auxiliary throttle valve occurs due to the presence of the collector capacity.